Docker Pull Python
The problem is that the image you are trying to pull does not contain a latest tag, only a v2 tag.
Change the first line in your Dockerfile to FROM rdempsey/python-scraper:v2 and everything should work fine.
You are pulling with latest tag which is not present at DockerHub. Try:
docker pull rdempsey/python-scraper:v2
You can see the version at https://hub.docker.com/r/rdempsey/python-scraper/tags/
Use a explicit version number (in this case v2) instead of the latest tag.